Preparation of modified elastomers

ABSTRACT

Disclosed is a method for crosslinking elastomers containing randomly distributed sites of conjugated olefinic unsaturation of which the crosslinks are comprised of chains of free radical polymerizable monomers.

BACKGROUND OF THE INVENTION

Curing of unsaturated polymers and grafting onto unsaturated elastomersis well known in the art. Such prior art produces either a nonrubberyproduct or a product not obtainable by the easily processable mixes ofthe present invention.

For example, U.S. Pat. No. 3,791,655 discloses a method for preparing ahard rubber compound by grafting a carboxamide onto polybutadiene in thepresence of a free radical initiator. Monomers such as stryrene andvinyl toluene were used to crosslink PVC in U.S. Pat. No. 3,725,714, buthere, as in the above aforementioned patent, the product is nonrubberyand the polymer is not a polymer containing randomly distributed sitesof conjugated olefinic unsaturation as in the present invention.

SUMMARY OF THE INVENTION

This invention relates to the graft curing of polymers containingrandomly distributed sites of conjugated olefinic unsaturation byreacting such polymers with a free radical polymerizable monomer and afree radical initiator. It has now surprisingly been found thatpolymeric chains of monomers can be grafted onto polymers containingconjugated olefinic unsaturation while simultaneously crosslinking theentire system into an integral mass. The crosslinks are comprised ofpolymeric chains of the chosen monomer. This overall process willhereinafter be referred to as graft curing. In particular, thisinvention is directed to elastomers containing randomly distributedsites of conjugated olefinic unsaturation; especially such elastomers asconjugated diene butyl rubber and terpolymers of ethylene, a C₃ to C₁₀alpha olefin and a polyene which on incorporation into the polymerdeposits therein sites of conjugated olefinic unsaturation.

Heretofore, certain forming and molding techniques were not compatiblewith high molecular weight conjugated olefinic unsaturated polymers inview of the fact that such polymers exhibited a high viscosity. Thisinvention enables one to use high molecular weight polymers containingconjugated olefinic unsaturation in such molding techniques as sheetmolding, lay-up fabrication and even relatively low clamp pressureinjection molding. Such techniques are now available to such highmolecular weight polymers in view of the fact that the crosslinking freeradical polymerizable monomer serves as a diluent in lowering theviscosity of the polymer.

DETAILED DESCRIPTION

The expression "butyl rubber" is used in the rubber industry to describecopolymers made from a polymerization reaction mixture having thereinfrom 70 to 99.5% by wt. of an isoolefin which has about 4 to 7 carbonatoms, e.g., isobutylene, and about 30 to 0.5% by wt. of a conjugatedmultiolefin having from about 4 to 14 carbon atoms, e.g., isoprene. Theresulting copolymers contain 85 to 99.5% by wt. of combined isoolefinand about 0.5 to 15% of combined multiolefin. The preparation of butylrubber is described in U.S. Pat. No. 2,356,128, which is incorporatedherein by reference.

The polymer backbone of commercial butyl rubber is made up primarily ofisobutylene units, with just a few percent of isoprene units. Theisoprene units contribute the small amount of unsaturation present inbutyl rubber. The basic equation is represented by: ##EQU1## whichcombine in the presence of Friedel-Crafts catalysts to form: ##EQU2##where x+z represent the number of isoolefin units incorporated in thebutyl rubber, while y represents the number of olefin units derived fromincorporation of the diene present, substantially as randomlydistributed units. The conjugated diolefin, isoprene, loses one olefiniclinkage upon its essentially random incorporation into the polymerbackbone.

Thus, butyl rubber, as presently produced, contains only a smallpercentage of unsaturation, in the form of the single double bondassociated with the isoprene residue which is incorporated more or lessrandomly throughout the polymer chain.

Butyl rubber can be produced containing conjugated unsaturation. Thegeneral formula may be represented by: ##EQU3## where x, y and z havethe values previously described, though at least one double bond may layoutside the linear backbone. This variation may be represented by theformula: ##EQU4##

This new butyl rubber has been termed "conjugated diene butyl",hereafter referred to as CDB, regardless of the structure of theconjugated unsaturation.

CDB is more completely described in U.S. Pat. No. 3,816,371 andcopending U.S. application Ser. NO. 465,479. One of the preferredmethods of preparing this butyl rubber is described in U.S. Pat. No.3,775,387, all of which are incorporated herein by reference.

The CDB, containing the conjugated-olefinic unsaturation, may beprepared by dehydrohalogenation of halogenated butyl rubber.

Halogenated butyl rubber has been developed in recent years and hascontributed significantly to the elastomer business. A method ofpreparing halogenated butyl rubber is described in U.S. Pat. No.3,099,644, which is incorporated herein by reference. Both chlorinatedand brominated butyl rubber are well known in the art. The formula forhalogenated butyl rubber is representable by: ##EQU5## where x, y and zhave the same values as for butyl rubber, described above, though thisstructure is but one of several which can be formed, depending on theconditions of halogenation, the halogenating agent used, etc.

The important feature depicted is that the halogen atom is on a carbonatom which is alpha to a double bonded carbon and hydrogen on the carbonatom next to that to which halogen is attached (i.e., on the carbon atombeta to the double bonded carbon).

Halogenated butyl rubber is commercially available and may be preparedby halogenating butyl rubber in a solution containing 1 to 60% by weightbutyl rubber in a substantially inert C₅ -C₈ hydrocarbon solvent such aspentane, hexane, heptane, etc., and contacting this butyl rubber cementwith a halogen gas for a period of about 2-25 minutes. There is thenformed the halogenated butyl rubber and a hydrogen halide, the polymercontaining up to one or somewhat more, especially in the case ofbromine, halogen atoms per double bond initially present in the polymer.This invention is not intended to be limited in any way by the manner inwhich butyl rubber is halogenated or dehydrohalogenated and bothchlorinated and brominated butyl rubber are suitable for use inpreparing CDB.

Illustrative of halogenated butyl rubber is Exxon Butyl HT 10-68 (achlorinated butyl rubber which before halogenation analyzes ˜1.8 mole %unsaturation and a viscosity average molecular weight of about 450,000).However, for the purposes of this invention, it is preferred that thebutyl rubber starting material have incorporated therein from about 0.5to 6 mole % of combined diolefin, more preferably 0.5 to 3 mole %, e.g.,about 2 mole %.

Conventional high molecular weight butyl rubber generally has a numberaverage molecular weight of about 25,000 to about 500,000, preferablyabout 80,000 to about 300,000, especially about 100,000 to about250,000, and a Wijs Iodine No. of about 0.5 to 50, preferably 1 to 15.More recent low molecular weight polymers are prepared to have numberaverage molecular weights of from 5,000 to 25,000 and unsaturationexpressed as mole %, of 2-10.

A particularly advantageous method of preparing conjugateddiene-containing butyl polymers comprises heating a solution ofhalogenated butyl rubber in the presence of a soluble metal carboxylate.Suitable metals are the polyvalent metals of Groups Ib, IIb, IVa andVIII, of the Periodic Table, having a relatively high first ionizationpotential and whose halides are to some extent soluble in thehydrocarbon reaction medium at the reaction temperature. Typical ofthese are zinc, iron, mercury, nickel, copper, tin and cadmiumcarboxylates.

Especially useful are the soluble carboxylic acid salts of zinc (e.g.,zinc salts of naphthenic or aliphatic carboxylic acids). While useful inpreparing the compositions of the present invention, potential toxicityproblems which could be encountered in practicing the present inventionmight limit the use of certain metals, such as cadmium and mercurysalts, for example.

In dehydrohalogenating the halogenated butyl rubber, zinc chloride isthought to be a by-product in the reaction. Zinc chloride, being aneffective Friedel-Crafts type catalyst, may lead to molecular weightdegradation or crosslinking of the halogenated polymers, depending onthe structure of the polymer, the solvent being employed, the reactiontemperature, etc.

This difficulty is overcome, in the instant invention, by having presentin the reaction zone a metal oxide, hydroxide or carboxylate whosehalogen salt is insoluble in the reaction medium.

It has been found that the mole percent of conjugated olefinicunsaturation in a typical dehydrohalogenated butyl prepared fromchlorinated or brominated commercial butyl rubber, ranges from about 0.5to about 3.0 mole %.

While the CDB may be crosslinked by a variety of reagents such assulfur, sulfur-containing curing agents, UV radiation, polyfunctionaldienophiles, and the like, there are several applications for the highreactivity rubber in which such cures are not suitable. Moreover, simplecrosslinking of the elastomer cannot supply the alterations invulcanizate properties provided by the graft curing technique.

Thus, if high molecular butyl is to be used for low pressure injectionmolding, conventional fabrication techniques are not suitable in view ofits excessive viscosity.

It will be readily evident to those skilled in the art that the practiceof this invention is not limited to butyl rubber; but, applies to anyelastomer containing randomly distributed sites of conjugated olefinicunsaturation.

Illustrative of such an elastomer containing conjugated olefinicunsaturation other than CDB, would be the elastomeric copolymer ofethylene, a C₃ to C₁₀ alpha olefin, and a 5,6-di-methylene-2-norborneneas taught in U.S. Pat. No. 3,681,309 which is incorporated herein byreference.

This elastomeric copolymer of ethylene may be prepared by first forminga monomer mixture containing ethylene as a first component, a C₃ to C₁₀alpha olefin as a second component, and a 5,6-dimethylene-2-norborneneas a third component, and then polymerizing this mixture in the presenceof a compound of a transition metal as catalyst and an organometalcompound as cocatalyst, thereby forming a copolymer of ethylene, a C₃ toC₁₀ alpha olefin, and a 5,6-dimethylene-2-norbornene, wherein thecopolymer contains conjugated residual unsaturation derived from the5,6-dimethylene moiety of said norbornene; and withdrawing saidcopolymer as product.

The ethylene used in preparation of this terpolymer may typically bepurified commercially available ethylene of greater than 99.98% purity,typically 99.98%-99.999%, say 99.99%. It may contain less than 0.02%,typically 0.001%-0.02%, say 0.01% non-olefinic impurities, and less than0.001%, say 0.0001%-0.0005% water.

The alpha olefin, also called a terminal olefin, may be a purifiedcommercially available C₃ to C₁₀ olefin having a purity of greater than99.98%, typically 99.98-99.999%, say 99.99%. It may contain less than0.02%, say 0.001%-0.02%, say 0.01% non-olefinic impurities and less than0.001%, say 0.0001%-0.0005% water.

Non-polar impurities, such as ethane or other hydrocarbons may bepresent, but for best results, polar compounds such as oxygen, water,carbon dioxide, carbon monoxide may be maintained at the indicated lowlevels in the ethylene and alpha olefin feeds.

The alpha olefin having three to ten carbon atoms, may be designated bythe formula R'-CH=CH₂ wherein R' is hydrocarbon and typically selectedfrom the group consisting of alkyl, alkaryl, aralkyl, and aryl. Mostpreferably R' may be a fully saturated alkyl including cycloalkyl. Alphaolefins may include typically:

                  TABLE I                                                         ______________________________________                                        propene            3-ethyl pentene-1                                          butene-1           octene-1                                                   pentene-1          3-methyl heptene-1                                         3-methyl butene-1  4-methyl heptene-1                                         hexene-1           5-methyl heptene-1                                         3-methyl pentene-1 6-methyl heptene-1                                         4-methyl pentene-1 3-ethyl hexene-1                                           heptene-1          4-ethyl hexene-1                                           3-methyl hexene-1  3-propyl hexene-1                                          4-methyl hexene-1  decene-1                                                   5-methyl hexene-1                                                             ______________________________________                                    

The preferred alpha olefin may be propylene, i.e. propene.

The polyene may include those inertly substituted compounds having theFormula I wherein the carbon atoms are designated by number for easyreference. ##EQU6##

In the Formula I, each of the R and R" groups may be hydrogen orhydrocarbon and preferably independently selected from the groupconsisting of hydrogen, alkyl, alkaryl, aralkyl, and aryl. When R or R"is alkyl, it may be methyl, ethyl, propyl, isopropyl, buty, hexyl,octyl, decyl, etc. When R or R" is alkaryl, it may be tolyl, xylyl, etc.When R or R" is aralkyl, it may be benzyl, etc. When R or R" is aryl, itmay be phenyl, naphthyl, etc. The preferred R and R" groups may be alkyland aryl having up to 12 carbon atoms.

In the preferred embodiment, the R groups may be hydrogen. In the mostpreferred embodiment, R and R" are hydrogen, and the composition is5,6-dimethylene-2-norbornene se (II).

Typical 5,6 - dimethylene - 2 - norbornene compounds which may beemployed may include:

TABLE II

5,6-dimethylene-2-norbornene

1-methyl-5,6-dimethylene-2-norbornene

1-ethyl-5,6-dimethylene-2-norbornene

1-butyl-5,6 -dimethylene-2-norbornene

7-methyl-5,6-dimethylene-2-norbornene

7-butyl-5,6-dimethylene-2-norbornene

1-cyclohexyl-5,6-dimethylene-2-norbornene

7-methyl-5,6-dimethylene-2-norbornene

7-propyl-5,6-dimethylene-2-norbornene

7-ethyl-5,6-dimethylene-2-norbornene

1-phenyl-5,6-dimethylene-2-norbornene

These materials may be readily available or they may be prepared byprocedures well known to those skilled in the art.

Formation of these copolymers may be effected by forming a mixture ofthe three components containing the following molar parts:

                                      TABLE III                                   __________________________________________________________________________                    Broad   Preferred                                             Component       Range   Range   Preferred                                     __________________________________________________________________________    Ethylene        1,000-2,500                                                                           1,250-1,900                                                                           1,700                                         Alpha olefin    1,600-7,500                                                                           2,000-3,300                                                                           2,500                                         5,6-dimethylene 2-norbornene                                                                   15-200 25-40   30                                            __________________________________________________________________________

Mixtures of these compounds may be used, i.e. more than one alpha olefinand/or more than one 5,6-dimethylene- 2-norbornene may be employed.Other compatible components, including those which are copolymerizableto form tetrapolymers may be present including e.g. aromaticmono-olefins such as styrene, etc.

The following may be representative of copolymers which may be preparedby the process of this invention:

ethylene/propylene/5,6-dimethylene-2-norbornene;

ethylene/propylene/1-methyl-5,6-dimethylene-2-norbornene;

ethylene/propylene/1-ethyl-5,6-dimethylene-2-norbornene;

ethylene/1-butene/5,6-dimethylene-2-norbornene;

ethylene/1-hexene/5,6-dimethylene-2-norbornene;

ethylene/4-methyl-1-hexene/7-methyl-5,6-dimethylene-2-norbornene;

ethylene/1-decene/1-cyclohexyl-5,6-dimethylene-2-norbornene.

Graft curing of the CDB is accomplished by reacting the CDB in thepresence of a free radical initiator with free radical polymerizablemonomers for a time long enough to decompose most of free radicalinitiator or convert most of the monomer to polymer. The monomerpolymerizes and these polymeric chains of monomer become the crosslinksconnecting the elastomeric chains. Although not wishing to be limited bytheory, it is believed that the generated polymeric chains may connectin any of the following ways: ##SPC1##

that is, the elastomer chains are crosslinked and the crosslinks arepolymeric chains of the monomer, M. Some M chains will connect 2 or moreelastomer chains or 2 or more points in a given elastomer chain. Some Mchains will not be connected to the network at all. Some will beconnected to the elastomer molecule at just one point and, therefore, bea simple graft.

Obviously, but not illustrated in the diagram, some elastomer chains maybe connected directly one to the other. The number of such connectionswill depend on the amount of monomer employed, its relative reactivity,etc.

It is preferred that the elastomers suitable for use in this inventionhave from about 0.15 to about 10 mole % conjugated olefinicunsaturation. The amount of free radical polymerizable monomer suitablefor use in this invention is preferably in aggregate at least 1 mole ofpolymerizable groups per mole of conjugated olefinic unsaturation in theelastomer.

A variation of the process would employ prereaction of the polymer witha polyfunctional active dienophile such as a di or higher acrylate ormethacrylate ester via Diels-Alder coupling. This would produce apolymer with active polymerizable groups pendant to the chain asdepicted below: ##EQU7## where R is a polyvalent hydrocarbon radical andn is the number of functional groups.

This modified polymer may then be cured directly with free radicalinitiators or diluted further with radical polymerizable monomers andgraft cured.

Also, it is within the scope of this invention to employ suchpolyfunctional monomers in minor quantities to adjust the viscosity ofthe mixture by pre-crosslinking the polymer containing conjugatedolefinic unsaturation to a point below the gelation point of the mixtureprior to conducting the graft curing operations.

Also, within the concept of this invention, nonpolymerizable functionalgroups may be implanted on the polymer molecule by pre-reaction of partof the conjugated olefinic unsaturation with dienophiles, such as maleicanhydride; acrolein; acrylic and methacrylic acids and acid chlorides;acrylic, methacrylic and maleic acid esters or amides containing atleast one other functional group (e.g. OH, NH₂, halogen, olefin, etc.).

Useful monomers for this invention may be selected from the list of freeradical polymerizable monomers shown in "Appendix A and Appendix B" ofthe book Copolymerization by George E. Ham, Interscience Publishers(1964) on pages 695 to 863, subject to the conditions that the monomerbe nongaseous, soluble and as stated above, polymerizable.

By nongaseous, we mean that the monomer or monomers employed must beliquids or solids at the mixing temperatures and hydrostatic pressuresemployed during mixing, normally at room temperature and atmosphericpressure.

By soluble, we mean that the monomer or monomers mixture must be solublein the amounts used in the polymer or polymer-inert diluent mixture atthe temperature at which graft curing is to be conducted, usually -20°to 150°C.

By polymerizable, we mean that the monomer or monomers employed must becapable of forming homo or copolymers of number average molecular weight≧500 at the graft curing temperature.

Illustrative of such monomers which are suitable for use in thisinvention and which we in no way wish to be limited thereto include:

A. the vinyl substituted aromatics such as styrene, divinyl benzene,trivinyl benzene, and vinyl naphthalene;

B. the ring substituted vinyl aromatics such as 1-vinyl-4-chlorobenzeneand 1-vinyl-4-tertiary butyl benzene;

C. the acrylic and methacrylic acid esters of alcohols and glycols orsubstituted alcohols or glycols, such as methyl methacrylate, octadecylacrylate, methyl acrylate and isobutyl methacrylate; and

D. the vinyl esters of simple or polycarboxylic acids, such as vinylacetate, vinyl benzoate, vinyl propionate, and vinyl undecanoate,divinyl azelate.

Polyfunctional monomers can also be incorporated with or in place of thefree radical polymerizable monomer. When polyfunctional monomers areused with the free radical polymerizable monomer, crosslinks areproduced within the monomer chains so that not only is the elastomercrosslinked via monomer chains, but the monomer chains themselves may becrosslinked as below: ##EQU8## where M is a free radical polymerizablemonomer and R(M')_(n) is a polyfunctional free radical polymerizablemonomer wherein n is the number of polymerizable groups.

Polyfunctional monomers, as used in this invention, are defined as thosemonomers containing two or more polymerizable groupings chosen fromthose groupings which define a simple monomer (only one polymerizablegrouping). For example, styrene would be a simple monomer and di- andtri- vinyl benzene would be corresponding polyfunctional monomers.Another example would be propyl methacrylate representing the simplemonomer and 1,3 propane diol dimethacrylate, 1,2-propanol dioldimethacrylate and trimethyl propane trimethacrylate representingcorresponding polyfunctional monomers. These polyfunctional monomers, tobe useful in this invention, would also be required to be liquid orsolid at room temperature and atmospheric pressure as indicatedpreviously.

The process disclosed in this invention enables one to vary not only thephysical properties but also the chemical properties of the product overa wide range, depending on both the amounts and the nature of theparticular monomers used.

The free radical initiators which are suitable for use in the presentinvention include irradiation; organic peroxides; organic hydroperoxidesand azo compounds.

Illustrative of some peroxides useful in this invention include thedialkyl and diacyl peroxides.

The dialkyl peroxides have the general structure R OO R', where R and R'can be the same or different primary, secondary or tertiary alkyl,cycloalkyl, aralkyl, or heterocyclic radicals. Included in this group ofperoxides which are suitable for use in this invention are dicumylperoxide, di-t-butyl peroxide, t-Butylcumyl peroxide and 2,5-Dimethyl-2,5-bis (t-butyl peroxy) hexane.

Diacyl peroxides have the general structure RC(O)OOC(0)R' where R and R'are the same or different alkyl, cycloalkyl, aralkyl, aryl orheterocyclic radicals. Illustrative of some diacyl peroxides suitablefor use in this invention are dilauroyl peroxide, dibenzoyl peroxide,dicetyl peroxide, didecanoyl peroxide, di (2,4-dichlorobenzoyl)peroxide, diisononanoyl peroxide and 2-methylpentanoyl peroxide.

As will be evident to those skilled in the art any organic peroxidewhich is useful in cross-linking polymers or initiating polymerizationis encompassed in the present invention.

The basis for choice of peroxide for use in this invention include suchthings as the half life of the peroxide at the mixing and/or curingtemperature and the compatability of the selected peroxide in thesystem.

Examples of hydroperoxides which are suitable for use in the presentinvention include t-butyl hydroperoxide, cumyl hydroperoxide,2,5-dimethyl-2,5 dihydroperoxyhexane, p-methane hydroperoxide anddiisopropylbenzenehydroperoxide.

Examples of some azo compounds which are suitable for use as freeradical initiators in this invention include diazoaminobenzene,N,N'-dichloroazodicarbonamide, azo dicarboxylic acid diethyl ester andazo bis (isobutyronitrile).

Irradiation suitable for use in this invention include alpha radiation,gamma radiation, uv radiation and electron beam radiation or any otherhigh-energy radiation regardless of the source of energy (photons,protons, electrons, neutrons, etc.).

Tertiary amines can also be used in this invention to promotedecomposition of the organic peroxide. To be suitable in this invention,the tertiary amine must be soluble in the mixture employed at curingtemperature. Illustrative of such suitable tertiary amines aretriethylamine, tributylamine, 2,4,6-tris (dimethylamino) phenol, and3,3,7,7-tetramethylbicyclo (3,3,0) octane.

Metal carboxylates may also be used in this invention to acceleratedecomposition of the peroxides to radical fragments. Illustrative ofmetal carboxylates suitable for use in this invention are thenaphthenates, octoates and tallates of metals selected from the groupconsisting of aluminum, cobalt, vanadium, copper, calcium, lead,mercury, zinc, manganese, magnesium, zirconium and iron.

It will be evident to those skilled in the art that a mixture ofperoxide with varying half life at a given temperature can be used tocontrol the polymerization reaction. Also apparent to those skilled inthe art is the mixing of conventional fillers, oils, etc. with theelastomer monomer mixtures of this invention.

This invention and its advantages will be better understood by referenceto the following examples.

EXAMPLES 1-3

A butyl polymer was collected by precipitation from plant feed cementprepared in the commercial chlorobutyl solvent replacement process(SRP). This butyl polymer contained about 1.8 mole percent unsaturationand displayed a Mooney viscosity of 66.5 at 100°C.

Three 31.5 g samples of vacuum oven dried precipitated SRP butyl werecut into small pieces and the pieces of each sample were put into aseparate 8 oz. ointment jar. To each jar, 13.5 g of styrene was added.The air in each jar was displaced by nitrogen; the jars were sealed andallowed to stand overnight. After said standing, the styrene becameimbibed by the butyl. These monomer swollen polymers were then mixed ina Brabender Plastograph as follows:

                  TABLE I                                                         ______________________________________                                        SAMPLE       No. 1      No. 2      No. 3                                      ______________________________________                                        Butyl + styrene                                                                            45.0 g.    45.0 g.    45.0 g.                                    Calcium stearate                                                                           0.45 g.    0.45 g.    0.45 g.                                    Lauroyl Peroxide                                                                           0.10 g.    0.20 g.    0.45 g.                                    ______________________________________                                    

Portions of these mixes (stored under nitrogen) were then heated (cured)under pressure between mylar film in a mold in a small electricallyheated press at 100°C. for 40 minutes or about 7 times the peroxidehalf-life. On removal from the mold, the specimens were white, opaqueand sticky to the touch despite the presence of calcium stearate, ananti-tack agent.

Immersion of pieces taken from the specimens in solvents revealed thatall disintegrated to yield a cloudy solution in cyclohexane and alldissolved in toluene (a solvent both for polystyrene and butyl) to yielda clear solution. Thus, there was no evidence of crosslinking and thepolystyrene formed was probably dispersed in particle sizes of the orderof the wavelength of visible light to cause the opacity of the samples.

EXAMPLES 4-6

In contrast to Examples 1-3, the polymer used here was CDB as opposed tobutyl. The CDB was prepared as previously described in thisspecification and contained about 1.30 mole percent conjugated diene.

Again separate 31.5 g. samples of the polymer (here CDB) were cut intosmall pieces and the pieces from each sample were placed in a separate 8oz. ointment jar. To each jar 13.5 g. of styrene was added. The air ineach of the 3 jars was displaced by nitrogen; the jars were sealed andallowed to stand overnight. After standing overnight, the styrene becameimbibed by the CDB. These monomer swollen polymers were then mixed in aBrabender Plastograph as follows:

                  TABLE III                                                       ______________________________________                                        SAMPLE       No. 4      No. 5      No. 6                                      ______________________________________                                        CDB + styrene                                                                              45.0 g.    45.0 g.    45.0 g.                                    Calcium stearate                                                                           0.45 g.    0.45 g.    0.45 g.                                    Lauroyl peroxide                                                                           0.10 g.    0.20 g.    0.45 g.                                    ______________________________________                                    

Portions of these mixes (stored under nitrogen) were then heated (cured)under pressure between mylar film in a mold in a small electricallyheated press at 100°C. for 40 minutes or about 7 times the peroxidehalf-life.

On removal from the mold these samples were transparent but displayedslight opalescence caused by the insoluble calcium stearate and "dry" tothe touch. Fluid immersion tests of these samples were also conductedand the results are shown below in Table III.

                  TABLE III                                                       ______________________________________                                        SAMPLE         No. 4     No. 5     No. 6                                      ______________________________________                                        Tensile, psi   540       375       420                                        Elongation, %  405       355       345                                        Stress at 300% E                                                                             290       270       325                                        Swelling Ratio.sup.(1) -%                                                     Insolubles.sup.(2)                                                            in Cyclohexane 5.33-92.15                                                                              4.81-95.2 4.40-97.2                                  in Methylethyl                                                                Ketone (MEK)   1.34-92.15                                                                              1.36-94.4 1.36-95.8                                  in Toluene               4.30-96.3                                            ______________________________________                                         .sup.(1) Swollen Wt./Dry Weight                                               .sup.(2) (Dry wt./original wt.) × 100                              

The above data show that the polystyrene chains are intimately boundinto the crosslinked network in view of the fact that the percentinsolubles are high in all of the solvents. Cyclohexane is a solvent forCDB, but not for polystyrene. Methylethyl ketone is a solvent forpolystyrene, but not for CDB. And toluene is a solvent for both CDB andpolystyrene.

Preparations like those above in which calcium stearate was omitted werecrystal clear. Thus, immobilization of the polystyrene chains bychemical attachment to the elastomer prevented formation of largepolystyrene aggregates or domains. As indicated by Table III, thecrosslink density of the elastomer increases as the peroxide level isincreased as evidenced by the decline in swelling capacity incyclohexane as the peroxide concentration is increased.

On the other hand, the swelling behavior of the polystyrene is littleaffected by the increase in peroxide as evidenced by the swellingcapacity in methylethyl ketone. This suggests that it is the polystyrenechains which form the crosslinks between the elastomer molecules andthat the chain junction points with the elastomer, per averagepolystyrene chain, are roughly comparable and may be relatively few innumber.

Having illustrated the profound differences between the behavior of apolymer containing a low level of simple olefinic functionality(Examples 1-3) and one containing a low level of conjugated dienefunctionality (Examples 4-6), we can proceed with other examples whichbroadly illustrate the scope of this invention.

EXAMPLE 7

Using the technique and procedure described in Examples 1-6, thefollowing ingredients were used:CDB 31.5 g.Styrene 12.0 g.Hexanedioldimethacrylate 1.5 g.(a polyfunctional monomer)Lauroyl peroxide 0.2g.Calcium stearate 0.45 g.

After press curing at 100°C. for 40 minutes, a dry, transparent butopalescent sheet was formed with the following properties:

                  TABLE IV                                                        ______________________________________                                        Tensile, psi         945                                                      Elongation, %        255                                                      Stress at 200% E     615                                                      Swell Ratio in Toluene                                                                             3.43                                                     % Insolubles         95.9                                                     Swell Ratio in MEK   1.28                                                     % Insolubles         92.6                                                     ______________________________________                                    

Comparing these data with those in Examples 4-6 in which the sameperoxide concentration was employed, it is clear that the overall systemin EXAMPLE 7 is more highly crosslinked and that the polystyrene chainsare themselves crosslinked as indicated by the lower swelling capacityin MEK. This Example clearly demonstrates the effect of employing apolyfunctional monomer along with a simple monomer in practice of thisinvention. Thus, while the polystyrene chains from crosslinks betweenelastomer molecules, these polystyrene chains can also be crosslinked asa result of copolymerization with the polyfunctional monomer.

EXAMPLES 8-9

Using the technique and procedure described in Examples 1-6, thefollowing ingredients were used:

                         (8)       (9)                                            CDB                  17 g.     17 g.                                          1,6 Hexanediol dimethacrylate                                                                      3.0 g.    3.0 g.                                         Primiol 355*         4.0 g.    4.0 g.                                         Silene EF**          1.0 g.    1.0 g.                                         Lauroyl peroxide     0.1 g.    --                                             ABIN                 --        0.05 g.                                         *A white oil                                                                  **A commercial calcium silicate                                          

Sample (8) was press cured at 100°C. for 40 minutes and sample (9) at110°C. for 40 minutes. The following properties were measured aftercuring:

                         (8)       (9)                                            Swelling Ratio in Toluene                                                                          3.03      3.24                                           % Insoluble          82.4      81.9                                       

From the above data it is evident that one gets a crosslinking curewhere only a polyfunctional polymerizable monomer is used as opposed toeither the use of only monofunctional monomers or a mixture ofmonofunctional and polyfunctional monomers.

EXAMPLES 10-21

Using a smaller mixing device but the same method of preparing samplesas described in Examples 1-7, a number of mixtures were prepared andtested. The data are indicated in Table V.

                                      TABLE V                                     __________________________________________________________________________    MISCELLANEOUS GRAFT CURING EXPERIMENTS                                                                               Tensile,                                                                           % Elonga-                                                                          Toluene Immersion Data       Ex.                                                                              CDB, g.                                                                            Monomer,g     Initiator,g.sup.(1)                                                                    Additives, g                                                                          psi.sup.(2)                                                                        tion.sup.(2)                                                                       Swelling                                                                              %                    __________________________________________________________________________                                                             Insolubles           (10)                                                                             15.75                                                                              Styrene, 5.06 L.P., 0.075                                                                            none    575  365  4.50    91.3                         Butyl Methacrylate, 1.68                                              (11)                                                                             15.75                                                                              Styrene, 3.88 L.P., 0.075                                                                            none    185  305  4.43    91.8                         Butyl Methacrylate, 3.88                                              (12)                                                                             15.75                                                                              Styrene, 5.07 L.P., 0.075                                                                            none    385  395  4.78    90.1                         Vinyl Propionate, 1.68                                                (13)                                                                             15.75                                                                              Styrene, 3.88 L.P., 0.075                                                                            none    240  470  5.23    90.3                         Vinyl Propionate, 3.88                                                (14)                                                                             15.75                                                                              Styrene, 5.07 L.P., 0.075                                                                            none    855  400  4.50    93.0                         Methyl Methacrylate, 1.68                                             (15)                                                                             15.75                                                                              Styrene, 3.88 L.P., 0.075                                                                            none    1385 365  4.19    95.2                         Methyl Methacrylate, 3.88                                             (16)                                                                             15.75                                                                              Styrene, 5.07 L.P., 0.075                                                                            none    555  375  4.56    92.2                         Ethyl Methacrylate, 1.68                                              (17)                                                                             15.75                                                                              Styrene, 3.88 L.P., 0.075                                                                            none    995  395  4.49    93.7                         Ethyl Methacrylate, 3.88                                              (18)                                                                             15.75                                                                              p-tert butyl  L.P., 0.075                                                                            none    195  260  3.96    92.5                         styrene, 6.75                                                         (19)                                                                             9.0  Styrene, 9.0  ABIN, 0.15                                                                             none    1235 620  9.48    81.7                         Methyl Methacrylate, 4.5                                              (20)                                                                             9.0  Styrene, 12.0 ABIN, 0.15                                                                             none    1605 200  2.71    99.3                         Trimethylolpropane-                                                           trimethacrylate, 1.5                                                  (21)                                                                             9.0  Styrene, 9.0  L.P., 0.10                                                                             Primol 355,                                                                   4.5     925  435  5.65    77.1                         Trimethylolpropane-                                                           trimethacrylate, 0.2   Calcium                                                                       Stearate, 0.2                                  __________________________________________________________________________     L.P. = Lauroyl Peroxide                                                       ABIN = 2,2'-azobisisobutyronitrile                                            Data obtained on 40'/100°C cured pads for L.P. initiated compound,     40'/110°C cured pads for ABIN initiated compound                  

These data demonstrate: (1) the concept of using mixed monomers to varyproperties of the cured elastomer; (2) the use of polyfunctionalmonomers to adjust properties; and (3) varying the concentration ofmonomer from about 42.9% to about 150% based on the amount of elastomeror from about 30% to 60% based on the amount of elastomer plus monomer.

Of particular interest are the last three examples (1g-21). Here highconcentrations of monomer were employed and in the last example ahydrocarbon oil was employed to produce a very low viscosity compound.Even so, the compounds cured into integral networks. Obviously, the oilpresent in the compound at Example 21 would be extracted when thespeciment was immersed in a solvent. This is evidenced by the(relatively) low percent insolubles for this example.

EXAMPLES 22-28

The following ingredients were added to each of 7 jars:CDB 21.0g.n-hexylmethacrylate 7.2 g.1,6-hexanedioldimethacrylate 1.8 g.

After the elastomer had soaked up the monomer, the mixtures weretransferred to a Brabender Plastograph and additives incorporated asindicated below:

    22 17.7 g Suprex Clay, 4.5 g zinc oxide, 0.3 g A-188,* 0.6 g stearic             acid                                                                       23 17.7 g McNamee Clay, 4.5 g zinc oxide, 0.3 g A-188*, 0.6 g stearic            acid                                                                       24 17.7 g Whitex Clay, 4.5 g zinc oxide, 0.3 g A-188*, 0.6 g stearic             acid                                                                       25 16.1 g Hydral 710, 4.5 g zinc oxide, 0.3 g A-188,* 0.6 g stearic acid      26 14.3 g Celite 270, 4.5 g zinc oxide, 0.3 g A-188,* 0.6 g stearic acid      27 18.3 g Mistron Vapor, 4.5 zinc oxide, 0.3 g A-188,* 0.6 g stearic             acid                                                                       28 13.4 g Hisil 215, 4.5 zinc oxide, 0.3 g A-188,* 0.6 g stearic acid          *vinyltriacetoxysilane                                                        To each of these were then added 0.2 g of lauroylperoxide.               

The blended mixtures were then cured by molding each sample separatelybetween Teflon coated aluminum foil for 35 minutes at 100°C. and thefollowing results were obtained:

                  TABLE VI                                                        ______________________________________                                        Swelling Ratio/% in Solubles                                                                        Tensile,  Elonga-                                       Compound                                                                              Cyclohexane                                                                              MEK        psi     tion,%                                  ______________________________________                                        22      1.97/99.4  1.16/99.0  1,000   105                                     23      2.03/99.1  1.17/99.2  905     110                                     24      2.04/99.0  1.16/98.9  990     110                                     25      2.27/98.7  1.19/98.7  820     125                                     26      2.15/98.5  1.17/98.7  735     100                                     27      2.04/99.3  1.16/99.0  1,025   125                                     28      1.69/98.3  1.16/98.2  1,360    80                                     ______________________________________                                    

From the above data, it is evident that the monomer chains constitutepart of the crosslinked network in view of the low degree of swellingand high modulus of elasticity. Since all the fillers were added on anapproximately equal volume basis, the reinforcing capacity of thefillers is indicated by the tensile strengths. Filler bonding to thepolymer is good in view of the fact that vinyl-triacetoxysilane reactswith any OH groups on the filler leaving the vinyl group free to enterinto the polymerization reaction. Other substituted silanes may also beused so long as at least one of the residues thereon can become involvedin polymerization and the others can react with OH groups on thepigment, film, glass, fiber or other surface. Similarly, oherpolymerization initiators, e.g., peroxides, may be used so that curingtime and temperature adjustments can be made at will. Also reinforcementcould be obtained by the inclusion of glass fibers either separatelytreated or treated in situ as were the pigments to insure intimatebonding between filler and matrix.

EXAMPLES 29 and 30

An EPDM containing randomly distributed sites of conjugated olefinicunsaturation was prepared by copolymerization of ethylene, propylene anda 5,6-dimethylene-2-norbornene. This polymer when analyzed showed anethylene content of 50 wt. %, a propylene content of 48.6 wt. % and adimethylenenorbornene content of 1.4 wt. %. The polymer was free of geland was completely soluble in toluene.

Compositions were prepared as follows:

    EXAMPLE          29          30                                               ______________________________________                                        EPDM             3.75 g.     3.75 g.                                          Styrene          1.37 g.     1.37 g.                                          Lauroyl Peroxide 0.05 g.     0.10 g.                                          ______________________________________                                    

After curing for 35 minutes at 100°C in a press the compositionexhibited the following properties:

                  TABLE VII                                                       ______________________________________                                        EXAMPLE          29          30                                               ______________________________________                                        Tensile, psi     650         700                                              Elongation, %    220         200                                              Swelling Ratio*  3.59        3.61                                             % Insolubles*    94.5        93.4                                             ______________________________________                                         *Immersion fluid was toluene                                             

These examples indicate that even at relatively low levels of conjugatedolefinic unsaturation (about 0.5 mole % conjugated olefin units), thehigh reactivity of the residues leads to successful graft curing asindicated by substantial insolubilization and low swelling ratios.

It is to be understood that this invention is not restricted to theforegoing examples which serve only to illustrate the present invention.Numerous variations may be devised without departing from the scope ofthis invention.

What is claimed is:
 1. A method of crosslinking conjugated diene butylrubber containing randomly distributed sites of conjugated olefinicunsaturation, which comprises reacting said elastomers with acrosslinking agent comprising at least 1 non-gaseous, soluble, freeradical polymerizable monomer in the presence of at least 1 free radicalinitiator.
 2. The method of claim 1, wherein the elastomer contains fromabout 0.15 to about 10 mole % of conjugated olefinic unsaturation. 3.The method of claim 2, wherein the free radical polymerizable monomer ismonofunctional.
 4. The method of claim 3, wherein the monofunctionalmonomer is styrene.
 5. The method of claim 2, wherein the free radicalpolymerizable monomer is polyfunctional.
 6. The method of claim 2,wherein the elastomer is crosslinked with a mixture of monofunctionaland polyfunctional free radical polymerizable monomers.
 7. The method ofclaim 2, wherein the free radical initator is selected from the groupconsisting of organic peroxides and organic hydroperoxides.
 8. Themethod of claim 7, wherein the decomposition of the free radicalinitiator is accelerated with a compound selected from the groupconsisting of tertiary amines and metal carboxylates of metals selectedfrom the group consisting of cobalt, vanadium, manganese, copper, leadand iron.
 9. The method of claim 2, wherein the elastomer is conjugateddiene butyl rubber.
 10. The method of claim 9, wherein the free radicalpolymerizable monomer is monofunctional.
 11. The method of claim 9,wherein the free radical polymerizable monomer is polyfunctional. 12.The method of claim 9, wherein the conjugated diene butyl rubber iscrosslinked with a mixture of monofunctional and polyfunctional freeradical polymerizable monomers.
 13. The method of claim 9, wherein thefree radical initiator is selected from the group consisting of organicperoxides and organic hydroperoxides.
 14. The method of claim 13,wherein the decomposition of the free radical initiator is acceleratedwith a compound selected from the group consisting of tertiary aminesand metal carboxylates of metals selected from the group consisting ofcobalt, vanadium, manganese, copper, lead and iron.
 15. The method ofclaim 1, wherein the elastomer is an elastomer containing randomlydistributed sites of conjugated olefinic unsaturation and activepolymerizable groups pendant to the elastomer backbone.
 16. The methodof claim 1, wherein the elastomer is an elastomer containing randomlydistributed sites of conjugated olefinic unsaturation andnon-polymerizable groups pendant to the elastomer backbone.
 17. Theproduct of claim
 2. 18. The product of claim 9.